Bis(η5-cyclopentadienyl)(2-{[(2-methoxyphenyl)imino]methyl}phenolato-κ3 O,N,O′)terbium

The air- and moisture-sensitive title compound was synthesized from tris(cyclopentadienyl)(tetrahydrofuran)terbium and 2-{[(2-methoxyphenyl)imino]methyl}phenol. Each Tb atom is coordinated by two cyclopentadienyl ligands in an η5-coordination mode and by one N and two O atoms of the organic ligand in a tridentate κ3 O,N,O′-mode.


Chemical context
Bis(cyclopentadienyl) complexes of rare-earth metals attract significant attention because of their important role in the development of organometallic chemistry of 4f elements (Schumann et al., 1995;Wedal & Evans, 2021;Evans, 2016). This type of complex is one of the first discovered organolanthanide classes (Maginn et al., 1963).
The vigorous interest in cyclopentadienyl complexes for the chemistry of rare-earth elements is mainly due to the simplicity of cyclopentadienyl ligand modification by replacing the hydrogen atoms of the five-membered ring with various organic fragments (Harder et al., 2013;Roitershtein, Puntus et al., 2018;Hou & Wakatsuki, 2002). Moreover, in the case of bis(cyclopentadienyl) derivatives such as (C 5 H 5 ) 2 LnX, the additional anionic ligand X À can be coordinated in a mono-, bi-or, as in the present case, a tridentate mode. Such a combination of ligands provides an extremely broad structural diversity for cyclopentadienyl derivatives (Edelmann & Poremba, 1997;Goodwin et al., 2018). This report describes the synthesis and crystal structure of bis( 5 -cyclopentadienyl) (2-{[(2-methoxyphenyl)imino]methyl}phenolato)terbium, which is a product of the partial protonation of the tris-(cyclopentadienyl)terbium complex with 2-{[(2-methoxyphenyl)imino]methyl}phenol (Fig. 1). ISSN 2056-9890

Structural commentary
The title compound (Fig. 2) crystallizes in the orthorhombic Pbcn space group (Z 0 = 1). Assuming that each cyclopentadienyl ligand donates three electron pairs, the terbium atom may be considered to be ennea-coordinated. Both cyclopentadienyl ligands are nearly symmetrically 5 -coordinated to the Tb 3+ cation. Thus, the Cp (centroid) -Tb distances [2.4207 (11) Å for the C1-C5 Cp ring and 2.4062 (10) Å for the C6-C10 Cp ring] are almost equal to the Cp (plane) -Tb distances [2.4196 (11) Å for C1-C5 Cp ring and 2.4054 (10) for C6-C10 Cp ring], and the C Cp -Tb bond lengths are similar within each ring (Table 1). At the same time, the average C Cp -Tb distance to the C1-C5 ring is longer by 0.011 Å than to the second Cp ligand. Such a slight asymmetry is caused by the presence of the tridentate asymmetric 2-{[(2-methoxyphenyl)imino]methyl}phenolate (L À ) ligand. Atoms of the ligand are situated in two planes formed by the following sets of atoms: O1, C11-C16, N1, C24 (r.m.s. deviation = 0.0167 Å ) and O2, C17-C23, N1 (r.m.s. deviation = 0.0333 Å ). The dihedral angle between these planes of 44.58 (5) indicates a perceptible loss of conjugation between two parts of the ligand due to the tridentate 3 N,O,O 0 -coordination mode. The bond redistribution within the ligand (see table in the supporting information) and the Tb-O and Tb-N bond distances (Table 1) are in good agreement with the expected predominant resonance form (see scheme) and with a significant localization of the negative charge on the O2 atom.
It should be noted that analogous compounds with the same L À ligand [(C 5 H 5 ) 2 Ln(O 2 NC 14 H 12 )] (Ln = Sm, Er, Dy, Y) were previously synthesized in low yields (Yousaf et al., 2000), and the determined crystal structure of the Sm complex is isostructural with that of the title compound.
Non-covalent interactions are negligible in the title compund.

Synthesis and crystallization
Synthetic operations were carried out in a glovebox under a purified argon atmosphere. THF was distilled from sodium/ The title compound with displacement ellipsoids drawn at the 50% probability level.  Figure 1 Synthesis of the title compound.
benzophenone ketyl, hexane was distilled from Na/K alloy. Tb(C 5 H 5 ) 3 (thf) was obtained according to a literature procedure (Wilkinson & Birmingham, 1954). A solution of 2-{[(2-methoxyphenyl)imino]methyl}phenol (0.230 g, 1.01mmol) in 5 ml of THF was added slowly to a solution of Tb(C 5 H 5 ) 3 (thf) (0.426g, 1.0 mmol) in 15 ml of THF. The reaction mixture was stirred for 24 h. The solution was concentrated under vacuum to a volume of ca 8-10 ml, and hexane (10 ml) was carefully layered on top of the resulting solution to initiate crystallization. Crystals obtained after several days were dried under dynamic vacuum for 1 h, yielding 0.315 g (0.61 mmol, 61%). The terbium content was determined by direct complexometric titration with the disodium salt of EDTA, using xylenol orange indicator (Vogel, 1966). Calculated for C 24 H 22 NO 2 Tb: Tb, 30.84%. Found Tb, 30.45%.
Single crystals suitable for X-ray diffraction study were taken from a vial with a crude product before drying under vacuum.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The structure was in general solved by dual methods (SHELXT; Sheldrick, 2015a). Positions of remaining non-H atoms were found from the difference electron density maps. All non-H atoms were refined aniso-tropically. The positions of hydrogen atoms were refined with U iso (H) = 1.5U eq (C) for methyl group and U iso (H) = 1.2U eq (C) for others.

Funding information
Funding for this research was provided by: Russian Science Foundation (grant No. 17-13-01357). Data collection: APEX2 (Bruker, 2016); cell refinement: SAINT (Bruker, 2016); data reduction: SAINT (Bruker, 2016); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018 (Sheldrick, 2015b); molecular graphics: Mercury (Macrae et al., 2020); software used to prepare material for publication: publCIF (Westrip, 2010). Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq